In order to increase the efficiency and the performance of gas turbine engines so as to provide increased thrust-to-weight ratios, lower emissions and improved specific fuel consumption, engine combustors are tasked to operate at higher temperatures. As the higher temperatures reach and surpass the limits of the material comprising the components in the combustor section of the engine and in the turbine section of the engine, new materials must be developed or methods of cooling the materials must be enhanced.
As the combustor operating temperatures have increased, new methods of cooling the high temperature alloys comprising the combustors and the turbine airfoils were developed. For example, ceramic thermal barrier coatings (TBCs) were applied to the surfaces of components in the stream of the hot effluent gases of combustion to reduce the heat transfer rate and to provide thermal protection to the underlying metal and allow the component to withstand higher temperatures. These improvements helped to reduce the peak temperatures and thermal gradients. Cooling holes were also introduced to provide film cooling to improve thermal capability or protection. Simultaneously, ceramic matrix composites were developed as substitutes for the high temperature alloys. The ceramic matrix composites (CMCs) in many cases provided an improved temperature advantage over the metals, making them the material of choice when higher operating temperatures were desired.
To compete with CMCs, additional improvements have been developed to allow metallic components to operate at temperatures that are comparable to the operating temperature of CMC components. For example, to counter the temperature advantage enjoyed by turbine components made from CMC materials, surface enhancements have been added to the metal components. These enhancements are referred to as turbulators and increase the cooling efficiency of the metal turbine components, allowing them to operate in higher temperature environments or conversely, with reduced cooling requirements. These turbulators increase the cooling efficiency of the component by increasing the surface area over which the channeled cooling air passes so that the metal component does not exceed its limits.
While in theory the temperature capability of turbine components made from CMC materials can similarly be improved by adding like surface enhancements, a cost effective process to apply these surface enhancements onto ceramic matrix composites previously did not exist. Attempts have been made to provide the surface enhancements in the form of turbulators to CMC turbine components by machining, but, as a result of the brittle nature of the ceramic, it is very susceptible to chipping and cracking during the machining process. Thus, it has not been feasible to fully take advantage of the higher temperature capabilities of components made from ceramic matrix composites. Without the economic incentive, the further development and incorporation of components made from ceramic matrix composites has not progressed.
What is needed is an effective process to apply surface enhancements such as turbulators to the surface of ceramic matrix composites.